The present invention concerns a method and a device for the measurement of physical parameters in an operating well of a deposit or underground fluid storage reserve.
In the case of underground storage of a fluid such as natural gas, control of storage performance involves access to data on the reservoirs and associated wells which are reliable and up to date. This is the case in particular with deposit pressure values which must be checked regularly for storage in water-bearing deposits.
At present, these quantities are most often evaluated on the basis of measurements made at the well head. Such measurements make it possible to have information on the situation at the bottom of a well only approximately, which may cause significant errors on storage performance forecasts.
Whether it is for sites in water-bearing deposits or for saline cavities, it is essential to be able to have information on physical parameters, particularly on the pressure, in the conditions at the bottom of an operating well, and not just at the well head.
It has already been proposed to introduce physical measurement sensors in an annular space defined between a central operating tubing and the outer cylindrical wall of the well. In this case, the sensors are connected to the surface by a wire link also situated in the annular space in which the fluid worked does not circulate. This solution enables measurement in real time of the well bottom conditions.
However, the sensor and the electronic circuits which are associated with it, which are integrated in the well structure, cannot be removed for maintenance or replacement without an operation of repair of the well structure itself being performed, which is particularly expensive since it requires removal of all or part of the well structure. In so far as the sensor and the associated electronic circuits are not situated in an easy-access zone allowing repair or exchange to be carried out rapidly, since any operation of positioning or depositing a sensor can be done only on the occasion of repair of the well, it is necessary, in order to obtain the required reliability and ensure continuity of measurements, to choose high-cost sensors and electronic circuits to meet the difficult environmental conditions, and to install a redundant number of sensors and electronic circuits.
It has further been proposed to install, in the interior itself of an operating tubing of a well, by cable work, a measurement module which can thus be arranged at the bottom of the well. The data are transmitted from the measurement module situated at the bottom of the well, to a transceiver situated at the surface in the vicinity of the well. Transmission is effected wirelessly between the buried module and the transceiver at the surface by electromagnetic radiation through the geological strata. Wireless transmission is however highly energy-consuming and imposes restrictions on the energy source (accumulator battery) incorporated into the measurement module.
Such a system can therefore be envisaged only for applications of limited duration and moreover has a relatively large overall size which constitutes an obstacle within the operating tubing. Furthermore, the wireless transmission system can be represented by a gigantic coaxial line. In such a coaxial line, the conductive core consists of the string of rods of the operating tubing, with its electrical properties, the internal insulator consists of the ground close to the well and the outer conductive casing consists of the ground situated at a greater distance from the well. It proves that the quality of transmission of the signal by such a wireless system is rather random, because it depends both on the type of structure of the operating tubing of the well and the resistivity of the geological formation to be traversed. The performance can thus vary considerably from one site to the next and within the same site, from one well to the next. Further, the choice of location of the sensor within the well is not very easy, since, in order for the emission of electromagnetic waves to be done in good conditions, the resistivity xcfx81 of the geological formation must be high enough in the vicinity of the well (xcfx81 greater than 10 ∩xc2x7m on average) and low at a certain point at the level of the sensor (xcfx81 less than 10 ∩xc2x7m over several meters).
Finally, there must be mechanical contact at the level of the measurement module containing the sensor, between the operating tubing and the well structure (casing), to prevent the measurement module from being electrically insulated from the geological formation. Such a measurement module therefore risks not functioning correctly, particularly on wells in saline cavities having a suspended central tubing.
The present invention aims to remedy the drawbacks of the prior-art systems and to make it possible to take reliable measurements of physical parameters within operating wells over a long period at low cost.
The invention further aims to facilitate the operations of positioning and depositing the most fragile parts of measuring devices, without it being necessary to carry out repair of the well structure.
These aims are achieved, according to the invention, owing to a device for the measurement of physical parameters in an operating well of a deposit or underground fluid storage reserve, which operating well includes an outer wall delimiting, with a central operating tubing of the well, an annular space in which is placed a protective sheath of an electrical link cable between a surface installation and elements arranged in the well, characterised in that it includes at least one compact, removable, sealed measuring subassembly arranged in a housing in communication with the interior of the central tubing and at least one compact, sealed connecting subassembly integral with the central tubing of the well and arranged at least partially in the annular space in the vicinity of said protective sheath in order to be connected to said electrical link cable and in that the sealed measuring subassembly and the sealed connecting subassembly have plane contact surfaces each associated with a half-transformer so as to form an inductive coupling between the measuring subassembly and the connecting subassembly.
The device according to the invention thus makes it possible to ensure in a damp environment a robust and reliable connection which is compact and enables the positioning and deposition of the measuring subassembly containing a sensor and the associated electronic circuits, by cable work within the operating tubing, from the surface, without requiring repair of the well structure.
The convenience of exchange of the removable measuring subassembly makes it possible to facilitate maintenance and to modify the configuration of the measuring subassembly according to requirements, which makes the system flexible and open-ended.
In the inductive coupling used within the framework of the device according to the invention, each half-transformer associated with a plane contact surface includes a magnetic circuit and a coil embedded in a solid material making it possible to withstand the forces of the pressure, such as a resin or a glass.
Advantageously, the half-transformers include thin welded non-magnetic metal sheets which constitute the plane contact surfaces and form part of sealed enclosures of the measuring and connecting subassemblies.
The measuring subassembly includes at least one sensor, an energy storage element and electronic circuits providing the interface between the half-transformer, the energy storage element and the sensor.
The electronic circuits include coding-decoding circuits and circuits for control of the power supply and for management of the information emitted by the sensor.
According to one particular embodiment, the measuring subassembly cooperates with positioning stops formed by the housing of the central tubing.
The measuring subassembly may include a profiled portion for positioning in the housing of the central tubing, while the connecting subassembly includes a profiled portion complementary to the profiled portion for positioning the measuring subassembly, to allow positioning of the connecting subassembly in the vicinity of the housing of the central tubing.
The connecting subassembly may traverse the wall of the housing of the central tubing in order to be situated partially in the annular space and partially in the housing in communication with the interior of the central tubing.
According to an advantageous embodiment, the electrical link cable cooperating with the connecting subassembly and the measuring subassembly forms a single-wire semi-duplex link for transmitting electrical signals alternately in descending fashion in the form of control signals and in ascending fashion in the form of data signals.
More particularly, the electrical link cable is adapted to transmit signals for electrical supply of the connecting subassembly and the measuring subassembly during the periods in which data signals are not transmitted.
The device according to the invention may include several measuring subassemblies associated with connecting subassemblies connected in parallel on the same electrical cable constituting a link in the form of a bus.
The invention also concerns a method for the measurement of physical parameters in an operating well of a deposit or underground fluid storage reserve, which operating well includes an outer wall delimiting, with a central operating tubing of the well, an annular space in which is placed a protective sheath of an electrical link cable between a surface installation and elements arranged in the well, characterised in that at least one sealed connecting subassembly arranged at least partially in said annular space and including a half-transformer is installed stationarily and integrally with the central operating tubing of the well, in the vicinity of the protective sheath and electrically connected to the electrical link cable, in that at least one compact, sealed measuring assembly provided with a half-transformer is introduced removably through the central tubing with the aid of a tool remotely controlled from the surface owing to a current-carrying cable and in that this measuring subassembly is positioned in a side pocket formed in the central tubing to which is fixed the connecting subassembly, in such a way that the measuring subassembly is coupled inductively to the connecting subassembly connected to the electrical link cable.
Advantageously, alternating low-frequency electrical signals for power supply of the measuring subassembly and data transmission and control signals are sent alternately an via the electrical link cable.